Should I use equal or unequal variance t test?
Welch's t-test: Assumes that both groups of data are sampled from populations that follow a normal distribution, but it does not assume that those two populations have the same variance. So, if the two samples do not have equal variance then it's best to use the Welch's t-test.Apr 11, 2021
Why do we use unequal variance?
Your prime goal is not to ask whether two populations differ, but to quantify how far apart the two means are. The unequal variance t test reports a confidence interval for the difference between two means that is usable even if the standard deviations differ.Jan 31, 2010
What is equal variance vs unequal variance?
The Two-Sample assuming Equal Variances test is used when you know (either through the question or you have analyzed the variance in the data) that the variances are the same. The Two-Sample assuming UNequal Variances test is used when either: You know the variances are not the same.Dec 21, 2013
What tests use unequal variance?
Welch's t-testIn statistics, Welch's t-test, or unequal variances t-test, is a two-sample location test which is used to test the hypothesis that two populations have equal means.
Why is unequal variance more conservative?
The conservative choice is to use the "Unequal Variances" column, meaning that the data sets are not pooled. This doesn't require you to make assumptions that you can't really be sure of, and it almost never makes much of a change in your results.Oct 22, 2018
Does equal variance mean normal distribution?
Is this the same as the variance to follow a normal distribution? It means that they are equal. No catch there, except that a hypothesis that (population) variances are equal can be consistent with (sample) variances not being exactly the same. Variance following a normal distribution would not be the same.Dec 5, 2013
Can you run at test with unequal sample sizes?
Even though you can perform a t-test when the sample size is unequal between two groups, it is more efficient to have an equal sample size in two groups to increase the power of the t-test. Welch's t-test is for unequal variance data.
What does equal variance mean in statistics?
Statistical tests, such as analysis of variance (ANOVA), assume that although different samples can come from populations with different means, they have the same variance. Equal variances (homoscedasticity) is when the variances are approximately the same across the samples.Nov 7, 2016
What does equal variance mean in t-test?
• Two-sample T-Test with equal variance can be applied when (1) the samples are normally distributed, (2) the standard deviation of both populations are unknown and assumed to be equal, and (3) the sample is sufficiently large (over 30).
What is the assumption of equal variance?
The assumption of equal variances (i.e. assumption of homoscedasticity) assumes that different samples have the same variance, even if they came from different populations. The assumption is found in many statistical tests, including Analysis of Variance (ANOVA) and Student's T-Test.Apr 25, 2021
When should I use the Welch's t-test?
Welch's t-test also known as unequal variances t-test is used when you want to test whether the means of two population are equal. This test is generally applied when the there is a difference between the variations of two populations and also when their sample sizes are unequal.
What is Bartlett's test?
Bartlett’s Test tests the null hypothesis that the samples have equal variances vs. the alternative hypothesis that the samples do not have equal variances. If the p-value of the test is less than some significance level (like 0.05), then we have evidence to say that the samples do not all have equal variances.
How to test ANOVA?
An ANOVA assumes that each of the groups has equal variance. There are two ways to test if this assumption is met: 1. Create boxplots. Boxplots offer a visual way to check the assumption of equal variances. The variance of weight loss in each group can be seen by the length of each box plot. The longer the box, the higher the variance.
How to test if two populations are equal?
A two sample t-test is used to test whether or not the means of two populations are equal. The test makes the assumption that the variances are equal between the two groups. There are two ways to test if this assumption is met: 1. Use the rule of thumb ratio. As a rule of thumb, if the ratio of the larger variance to the smaller variance is less ...
What is linear regression?
Linear regression is used to quantify the relationship between one or more predictor variables and a response variable. Linear regression makes the assumption that the residuals have constant variance at every level of the predictor variable (s). This is known as homoscedasticity.
What is test for equal variances?
Use a test for equal variances to test the equality of variances between populations or factor levels. Many statistical procedures, such as analysis of variance (ANOVA) and regression, assume that although different samples can come from populations with different means, they have the same variance.
Which test should I base my conclusion on?
By default, Minitab's Test for Equal Variances command displays results for Levene's method and the multiple comparisons method. For most continuous distributions, both methods give you a type I error rate that is close to your specified significance level (also known as alpha or α). The multiple comparisons method is usually more powerful.
The F-test and Barltett's test
Instead of the multiple comparisons method and Levene's method, you can choose to display results for the test based on the normal distribution. If you have only 2 groups or factor levels, then Minitab performs the F-test. If you have 3 or more groups or factor levels, then Minitab performs Bartlett's test.
